Converging evidence supports a correlation between sustained stress and the onset or exacerbation of symptoms for Irritable Bowel Syndrome. Some studies indicate a correlation between intense stress and persistent alteration of visceral sensitivity. A better understanding of the mechanisms by which stress can lead to sustained visceral hyperalgesia may have important implications for therapeutic approach of functional bowel disorders. We previously showed that chronic psychological stress in rat leads to sustained increase of visceral nociception that involves NK1 receptors (NK1R) activation in the spinal cord. The current proposal is based on the general hypothesis that spinal up-regulation of NK1Rs observed in this model is mediated by the interplay of peripheral immune activation and increased signaling to spinal dorsal horn (DH) neurons via primary afferent fibers, spinal microglia and descending spinal pathways. We will focus on the role of signaling molecules derived from primary afferent fibers in the regulation of NK1R gene expression in spinal DH neurons. We will use a combination of quantitative real time PCR, immunohistochemistry, electrophoretic mobility shift assay, Western blot and in vivo pharmacological approach to identify the mediators involved in this regulation. In aim 1, we will evaluate the time course correlation between stress-induced colonic immune activation, primary afferent fibers stimulation and subsequent increase of NK1Rexpression in DH neurons. In aim 2, we will address the potential correlation between stress-induced up-regulation of spinal NK1R and activation of the transcription factors CREB and NFkappaB in the same neurons. In aim 3, we will evaluate, through pharmacological treatment, the functional contribution of primary afferent neurons in stress-induced activation of CREB and NFkappaB, and increased expression of NK1R. The specific role of CGRP and spinal TNFalpha in this modulatory effect will be assessed. This proposal is expected to provide new insights into the mechanisms by which stress affects the processing of visceral nociception.